The invention is concerned with covers for large tanks, particularly tanks in sewage treatment processes, for containing malodorous gases.
Tank covers of the general type with which this invention is concerned are shown in U.S. Pat. Nos. 6,151,835, 6,012,259, 5,941,027, 5,911,662, 5,617,677, 5,545,358 and 5,325,646. These patents are incorporated herein by reference.
Increasingly there is a need for covers to enclose in-ground and above ground tanks used for storing waste materials including sewage, chemical sludge, petroleum products and other volatile and odorous materials. The materials generally are stored for later disposal or treatment in such tanks. Such a cover must be substantially gas tight for controlling odors in the vicinity of the tank site and for trapping potentially hazardous gases. Often the gases are withdrawn for cleaning, such as by biofiltration, placing a slight vacuum in the airspace above the tank. The tank should be substantially seated to minimize intrusion of air.
A tank cover is generally too large to be conveniently or cost effectively shipped in an assembled form from a manufacturer to the site of the tank. Because of this, tank covers for relatively large tanks are generally shipped as components and assembled at the site.
Prior art tank covers made of steel are heavy and expensive even to ship in component form. Further, such covers usually require welded connections and bolted connections in their assembly. As such, skilled personnel may be necessary to carry out the assembly, and the assembly process may be lengthy and costly. Some prior tank covers have been formed of sheet metal panels assembled at the site.
It is a purpose of the present invention to produce a highly modular tank cover system which requires very few fasteners and which allows for thermal expansion and contraction movement while still maintaining an almost complete gas seal.
The invention accomplishes these goals with unique metal extrusions which are assembled on-site in a modular system that is easily put together, with almost no fasteners and with other features providing for efficiency in installation and an effective substantially gas tight seal.
The system includes spanning beams of the appropriate size and spacing for the tank span to be covered. This may be, for example, approximately 12 feet to over 20 feet. Such span lengths can overlap with those addressed by the tank cover structure in U.S. Pat. No. 6,012,259, and can extend to greater lengths with larger beams or closer beam spacing.
In the system of the invention, a modular and nearly fastener-free cover system, substantially gas tight, is provided for open-top tanks which may be of the types described above. An important component is a gutter extrusion which includes a elongated gutter and flanges with sealing gaskets for engaging the top surface of the concrete on the tank as well as the inner wall of the tank several inches below the top. The gutter extrusion has gas seals at each of these two contact areas. The gasket seal which bears against the inner wall of the tank preferably comprises a structural member as well as a seal, helping hold the flange of the gutter extrusion from the tank wall. The seal preferably is pleated, with a type of bellows configuration, allowing the seal to compress to varying degrees on an irregular concrete surface, while still maintaining a seal. This and other seals may advantageously be formed of multi-durometer Santoprene.
The gutter strip is secured to the tank structure by a series of hold-down clips which are spaced apart at intervals, primarily at positions adjacent to the series of beams. These hold-down clips advantageously are extrusions, cut to the desired width (e.g. about 4 inches), with interlocking structure for sliding interlocking engagement with the gutter extrusion upon assembly. The cross section of the hold-down clip is configured to mate with the cross section of the horizontal flange on the gutter strip. On assembly to the tank, these hold-down clips are secured into the concrete using concrete anchor bolts, at a position somewhat removed from the tank edge, e.g. about 5 inches away. This provides for a stronger concrete anchoring by removing the anchor from near the edge of the concrete, and also helps avoid problems with other structure existing around the tank, such as handrails. Further, the bolt hole in the hold-down clip for receiving the anchor bolt preferably is angled such that the bolt is assembled obliquely from the outside, at an angle which may be about 15xc2x0 to 30xc2x0. This further aids in assembly by avoiding problems with handrails and other structure, and also helps draw the clip into firm engagement with the gutter strip. The purpose of the clips is to structurally prevent the gutter strips from pulling or tipping inwardly into the tank.
It is an important feature that the gutter is secured only with fasteners entering into the horizontal surface of the concrete, without requiring any fasteners to be secured into the vertical face of the tank, providing for considerably easier installation and avoiding the requirement that the installer enter the tank.
The gutter extrusion is thus cantilevered over the tank. Structural spanning beams rest on a platform at the inward side of the gutter extrusion, the entire extrusion having a relatively large width, e.g. 7 inches to 12 inches, and preferably about 10 inches to 11 inches, and extending over the tank about 8 inches to 9 inches in one preferred embodiment. These dimensions of course depend on the scale of the tank cover project, but the preferred dimensions will serve spans of a length somewhat more than 20 feet.
The manner which the spanning beams are supported on and secured to the gutter extrusion forms an important feature of the system. Thermal expansion and contraction are encountered to a considerable degree in large tank covers, primarily cause by changes in external atmospheric conditions. A beam of 20 feet or more can exhibit a length difference of xc2xc inch to xc2xd inch, between extremes of temperature. Importantly, the beams in the system of the invention are not secured to the gutter extrusions by fasteners, but instead are retained by a unique connection which allows for thermal expansion/contraction (length of the beam) and for movement in the perpendicular direction as well. This connection comprises a hold-down member which assembles slidingly into the gutter extrusion, at the side of the extrusion inboard of the tank. The gutter extrusion is formed in a preferred embodiment with a xe2x80x9ckeyxe2x80x9d shape which receives the slidable hold-down member by end assembly, such that the hold-down member cannot pull upwardly out of the gutter extrusion. Various such slidable, interlocking shapes can be used. The slidable hold-down connection member allows the beams to be moved to the appropriate positions on assembly, and also allows for other shifting in position which may occur due to thermal expansion and contraction affects.
The decking of the tank cover system preferably is formed of assembled extrusions (e.g. aluminum extrusions), similar to what is shown in U.S. Pat. Nos. 6,151,835, 6,012,259, 5,941,027, 5,911,662 and 5,617,677, referenced above. These preferably aluminum extrusions are assembled in substantially sealed relationship in panels, each panel resting on two of the spaced apart beams. The panels may be formed of interlocked deck slats extending in a direction perpendicular to the beams, with panel end members attached to edge deck planks and having flanges extending outwardly for sealing, and channel sections extending perpendicular to the deck planks and parallel to the main beams, receiving the ends of the deck planks, and with flanges which extend outwardly to rest on the beams. Gasket seals are positioned between the top of the beam and the flange of the panel. In a preferred embodiment, these gasket seals are slidingly connected to the tops of the extruded beams, in an interlocking connection, and with each gasket seal having two main ribs extending in parallel, each rib positioned to engage the underside of a flange from the deck panel.
For sealing the space at ends of the main beams, extruded flashing is secured to the gutter extrusion. These flashing components are continuous along sides of the tank, running perpendicular to the lengths of the beams. The flashing components may be Z-shaped, with a bottom flange having an interlock gasket seal for engaging downwardly against an outer end of the beam platform of the gutter extrusion. This component is secured down to the gutter extrusion, and tapered, self-tapping screws are advantageously used.
The upper flange of the flashing member retains a further gasket on its upper surface, and this is for sealing engagement with the overhanging flanges of the deck panels that extend in this direction. The edge of the sealing gasket abuts against the ends of the gasket seals which are secured to the tops of the beams, providing a part of the system gas seal, which is substantially air tight.
Another component of the assembly is a cap which is used on top of each beam, running parallel to the beam lengths. The cap, which may be about one-quarter inch thick and about one inch or so wide and formed of stainless steel, has left and right edges which clamp down against the edges of the two adjacent panels on either side of the beam, compressing the overhanging flanges of those panels down against the beam top gasket. The caps may be secured to the beam by self-tapping screws.
Accordingly, the tank cover system of the invention provides versatility in serving a wide variety of tank sizes, provides for easy and efficient assembly, substantially avoids fasteners and particularly avoids rigid connections between the beams and the peripheral beam support, makes wide allowance for thermal expansion and contraction, and provides a high integrity gas seal. These and other objects, advantages and features of the invention will be apparent from the following description of preferred embodiments, considered along with the drawings.